1. Field of the Invention
The present invention relates to a multi-laser system, and more particularly, to a multi-laser system capable of selecting a laser beam, from among various kinds of laser beams emitted from a pair of laser oscillators, most suitable for each of the materials of a substrate to be processed.
2. Description of the Related Art
Typically, laser systems transmit a laser beam emitted from a laser oscillator by using a laser beam transport means (for example, a reflection mirror, a beam expander, a scanner pair, a scan lens, etc.) and then perform an operation, such as drilling, marking, or cutting, by projecting the laser beam onto a substrate that is to be processed.
FIG. 1 is a schematic diagram of a conventional laser system, and FIG. 2 illustrates a cross-section of a substrate 2 processed using the conventional laser system illustrated in FIG. 1.
Referring to FIGS. 1 and 2, in the conventional laser system, 50% of a laser beam emitted from a laser oscillator 10 and incident upon a beam splitter 20 passes through the beam splitter 20, and the other 50% thereof is reflected by the beam splitter 20. The laser beam reflected by the beam splitter 20 passes through a scanner pair 41 and a scan lens 50 along a first path 1a and is radiated on a substrate 2, and the laser beam that penetrated the beam splitter 20 is incident on a reflection mirror 30, passes through a scanner pair 42, and the scan lens 50 along a second path 1b and is radiated on the substrate 2.
During a processing operation based on such a conventional laser system, absorptance, which depends on wavelength of the laser beam, of the materials of a substrate to be processed should be first considered. The substrate, formed of different materials, shows different reactions in view of a photo-thermal effect, a photo-chemical effect, and a photo-mechanical effect according to the wavelength of projected laser beams. Accordingly, a selection of laser beams that allow for a most suitable processing according to the materials of the substrate is important in performing a good-quality process.
For example, as shown in FIG. 2, when the substrate 2, which is a stack of a SiO2 layer 2a on a Si layer 2b, is processed using a laser beam emitted from the laser oscillator 10 and having a wavelength in an ultraviolet (UV) ray band, the quality of the process may not be good because the SiO2 layer 2a and the Si layer 2b have different optical characteristics with respect to the wavelength of the laser beam. In other words, since the SiO2 layer 2a transmits most of incident UV light and the Si layer 2b absorbs a high portion of the UV light, the laser beam in the UV ray band and incident upon a top surface of the substrate 2, passes through the SiO2 layer 2a and is absorbed by a top surface of the Si layer 2b. In this way, the substrate 2 is processed. Accordingly, heat and gas generated due to processing are accumulated at a boundary between the SiO2 layer 2a and the Si layer 2b, and an explosion occurs due to the accumulated heat and gas. This leads to a phenomenon where the quality of a processing operation using laser degrades.
With recent trends toward a rapid development in the semiconductor industry and an increase in the demand of a new field, a case where a substrate formed of a new material not used before needs to be processed or a substrate formed by stacking materials used before needs to be processed is increasing. However, as described above, when two or more materials needs to be processed using a laser having a single characteristic, such as, a fixed wavelength, good-quality processing is not guaranteed due to a difference between the optical characteristics of the two or more materials.